Burned Up Over Burnouts

Compressor burnouts can impact an entire HVACR system, including condensers and coils. But such burnouts have a number of myths attached to them:

Myth No. 1: “Acid can never be totally removed from a system after a compressor burnout.”

Myth No. 2: “Replacement compressors are likely to burn out too because their quality is lower than OEM equipment.”

Myth No. 3: “Replacing just the compressor or condenser after a burnout will remedy the acid situation.”

Burnouts inevitably involve acid. It’s the acid and how to handle it that propagates these myths.

The main question facing service techs is should (and can) the acid be removed or should the entire system or parts of it be replaced?

On large systems of 5 tons or more, complete acid removal is a normal service procedure because system replacement is typically cost-prohibitive.

Commercial system techs also perform acid checks during routine or yearly maintenance to help pinpoint growing problems that could prematurely shorten the life of the equipment.

Techs that work on smaller appliances or central a/c systems, however, may not understand the importance of performing acid checks.

Routine acid checks every year will frequently surface acid problems in older, inefficient units - especially in light of the fact that industry statistics indicate one out of every 10 acid checks turn up an acidic system. A proposition to replace it will not only help the customer in the long run, it will also produce more work for the service tech.

ACID REMOVAL

That being said, even if a customer can’t afford to do a system replacement, total acidity can be removed with several service steps. Probably the most important step is installing a filter-drier on the suction line and changing the existing filter-drier on the liquid line.

Most service techs realize the importance of the liquid line filter-drier replacement, but the perception exists that a suction line filter-drier isn’t needed because manufacturers typically don’t install them. Because the suction line filter-drier is positioned downstream of plumbing components and the liquid line filter-drier, it’s essential in trapping burnout contaminants just prior to the compressor inlet.

Installing two new filter-driers isn’t the end-all to acid problems, however. Typically, there’s approximately 2 percent of the old, highly acidic oil residing in a cleaned-up system after a burnout.

After installing the replacement compressor, that residual 2 percent of the old oil gets flushed into its sump even despite the presence of a new suction line filter-drier. Once that acid is flushed into the sump, it becomes diluted into the total oil charge and is slowly recirculated. Unfortunately, acid tends to grow exponentially within a system (two units becomes four units and then four units becomes 16 units, etc.) until it once again leads to another compressor burnout.

Using an acid flush poured into an injector and then circulated into the system while it’s operating can not only vaporize present acids and flush them to the filter-drier, but also remains in the system and continues to work as acid occurs. (Courtesy of Mainstream Engineering.)

REPLACEMENT COMPRESSORS

This residual acid leads us to Myth No. 2, that replacement compressors are poor quality substitutes for the OEM compressor. It’s true that replacement compressors many times burn out quickly, but it’s not due to quality. Instead, it’s usually due to residual acid that wasn’t removed during system cleanup.

Thus the fact that many service techs skip changing the filter-drier looms even larger in regards to residual acid and its removal. Removing the filter-drier does increase labor on a service call because it takes about the same amount of time as changing out a condenser, but the implications are too significant to ignore. Confirming the presence of residual acid by using a 10-second litmus paper test such as QwikCheck™ or some other chemical acid check will help pinpoint most potential burnouts altogether.

In fact, some contractors are offering their service techs $1 for every system they check for acid because they know that one of out of every 10 acid checks will turn up a problem that produces system replacement or acid removal business.

The unwillingness of an owner to replace a system despite its contamination can produce extra profits by eliminating the acid in the system with an acid remover or neutralizer. It’s a win-win situation because the contractor makes extra money for the acid treatment and the property owner gets a better operating system that will last longer. The typical refrigerant acid test doesn’t need an oil sample and takes just seconds to perform on an operating system.

Furthermore, not checking for acid on yearly service checkups is really a disservice to the customer, not to mention a loss of potential revenue for the service tech. A highly acidic system will most likely fail a few months later. Customers will see this failure as the service tech’s incompetence and will call a different contractor. Or worse yet, the unit will most likely fail on the hottest week of the year when the service company is inundated with “no cooling” calls. Impatient customers will call a different contractor every time.

REPLACING COMPRESSORS AND CONDENSERS

The third myth involving acid is that replacing the compressor and condenser solves an acid problem after a burnout. Unfortunately, acid usually still resides in the piping and the evaporator. Flushing products can help rid the system of contaminants, however not all acid flush products are the same. Water-based flushing products, for example, aren’t recommended because moisture can remain in the system. One reason for evacuation is to remove all moisture, so why introduce moisture from another source?

Other flushing compounds are essentially a mixture of halocarbons and alcohol. Some of these chemicals remain in a system and contaminate the new oil and refrigerant charge. Additionally, this residue negatively affects oil lubricity and viscosity, which potentially reduces compressor life and invalidates its warranty. Halocarbon’s presence in the oil also classifies it as a hazardous material and is subject to costlier disposal fees.

Acid neutralizers are helpful in removing the caustic effects of acid on piping and the evaporator; however, one disadvantage is determining the correct dosage. Too little neutralizer will allow trace amounts of acid to remain in the system, which will eventually do damage. Too much neutralizer can produce a chemical imbalance that’s just as caustic as the acid itself. Technicians also need to be aware that the process may produce salt water. The water is removed by the filter-drier, but the salt may remain as a contaminating residue in the system.

The advantage of neutralizers is easy application. Since it’s a liquid that never turns into a vapor, a neutralizer can be poured into the compressor, the lines are brazed, a vacuum is pulled, and the system gets charged with refrigerant.

Another type of acid remover is a flush product that vaporizes acid and moisture, which eventually becomes entrapped in the filter-drier. A product on the market for this is QwikShot®, which comes in ½-ounce bottles per 5 tons of refrigeration. When used properly, no contaminating residue is left behind because the acid is vaporized.

The disadvantage of flush products is that it takes a little bit more time because the steps vary from the neutralizing method. For example, an acid flush product isn’t added until after the system is put together, charged with refrigerant, and operating. Only then can the flush be added with a proprietary injection tool. Pouring in the acid flush as one might do with the neutralizing products before brazing, evacuating, recharging, etc., will simply boil all the flush product away during evacuation and leave the system susceptible to the residual acid again.

FILTER-DRIER FACTOR

Regardless of what neutralizing and flush products are used, the filter-drier should always be changed for long-term operation reasons. The filter-drier will trap acids and moisture for a long time. Changing the filter-drier simply gives the system a fresh start and the full capacity to handle trace acids that occur in the next five years or more.

If acid is treated or the system is replaced, it’s a good practice to perform frequent service calls until future acid tests prove negative.

While the replacement versus repair philosophy might produce some short-term business for a service company, odds are that customers will eventually gravitate toward the competition that uses preventive maintenance methods and preserves equipment for the long term.

Publication date: 06/04/2007

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Robert Scaringe is president of Mainstream Engineering, Rockledge, Fla., and has been involved in the development of advanced vapor-compression heat pump systems for more than 33 years. He currently has more than 70 HVAC-related patents. More information can be found at www.qwik.com or www.mainstream-engr.com.